Method for minimally invasive treatment of unstable pelvic ring injuries with an internal anterior fixator and posterior iliosacral screws

ABSTRACT

The instant invention is a novel method for definitive pelvic stabilization. The method uses the already established principles of anterior external fixation combined with internal hardware placed in a minimally invasive fashion. Pedicle screws are affixed to the ilia and a rigid, bowed fixation rod is connected between the pedicle screws. Preferably the pedicle screws are attached to the supra-acetabular area of each of the ilium of the pelvis and the fixation rod is bowed anteriorly away from the pelvis.

FIELD OF THE INVENTION

The instant invention relates generally to methods and apparatus for thetreatment of unstable pelvic fractures. More specifically the inventionrelates to a method and apparatus for minimally invasive treatment ofunstable pelvic ring injuries using an internal anterior fixator andposterior iliosacral screws.

BACKGROUND OF THE INVENTION

Unstable pelvic fractures typically occur as a result of high-energyinjuries such as automobile accidents, falls and the like. Even in thisage of modern polytrauma care, acute pelvic fractures are potentiallylethal. In the past, such injuries were treated without surgery.However, recovery to completely normal functionality was the exceptionrather than the norm. In more modern times, unstable pelvic fracturesare treated surgically with a number of techniques depending on the typeand extent of the fracture(s).

The pelvis consists of three major bones (two ilium and the sacrum) andsome minor bones joined together in a ring shape and held by strongligaments, See FIG. 1. General characteristics of pelvic fractureinclude severe pain, pelvic bone instability, and associated internalbleeding. Devices and methods used to treat fracture of the pelviscurrently fall under two general classifications; internal fixation andexternal fixation. Combinations of both techniques are frequently chosenfor certain fracture patterns.

Internal fixation is typically utilized when the patient exhibitsunstable posterior pelvic fractures. Internal fixation refers to platesand screws applied directly onto the fracture sites after realignment.See, for example, U.S. Pat. Nos. 4,454,876; 5,108,397; 6,340,362 and6,440,131. This type of fracture tends to be more complex with itinvolving multiple bony structures. Internal fixation addresses theseclinical issues through open reduction and correction of misaligned bonesegments that are subsequently stabilized with a wide variety of plateand screw methods.

Anterior pelvic fractures or hemodynamically unstable patients arecandidates for external fixation. Pelvic external fixation consists ofpins usually inserted into the iliac bones and then connected togetherby clamps and bars. See, for example, U.S. Pat. Nos. 4,292,964;4,361,144; 5,350,378 and 6,162,222. External fixation methods consistsof stabilizing the pelvic ring with a rigid framework residing outsidethe patient's body that is connected to the patient's pelvis viamultiple pins that penetrate through the patient's soft and hardtissues. Several frame types are currently utilized. Two of the morewidely deployed devices for external pelvic stabilization are theHoffmann 2 Inverted “A” Frame and the Ganz Pelvic C Clamp.

The application of external reduction and fixation for pelvic fracturesis advantageous compared to internal reduction and fixation due to itsspeed of deployment and lower level of technical training required forutilization. The primary disadvantages of external fixation of pelvicfractures include high risk of pin tract infections, and general patientdiscomfort. Also, the external frame physically blocks subsequentsurgery on the abdomen and they are frequently difficult to fit to obesepatients.

The instant inventor has developed a novel method using the alreadyestablished principles of anterior external fixation. By combining theseprinciples with internal hardware placed in a minimally invasivefashion, this technique allows for definitive pelvic stabilizationwithout having the issues and co-morbidities of an external fixator(i.e. interfering with other procedures, pin care, patient acceptance,later conversion to internal fixation, etc.)

SUMMARY OF THE INVENTION

The present invention comprises a surgical method for minimally invasivetreatment of unstable pelvic ring injuries comprising the steps of:affixing at least one fixation means to each ilium of the pelvis; andattaching a rigid, bowed subcutaneous fixation rod to at least one ofthe fixation means on each ilium.

The fixation means are preferably affixed to the supra-acetabular areaof each of the ilium of the pelvis. The fixation means preferably is apedicle screw. The pedicle screw is affixed by: creating a longitudinalincision centered between the Anterior Inferior Iliac Spine (AIIS) andthe Anterior Superior Iliac Spine (ASIS); bluntly dissecting through thesoft tissues; using fluoroscopic imaging to identify thesupra-acetabular starting point for the pedicle screw; opening thecortex of the ilium at said starting point with a drill; establishing acorridor between the inner and outer cortices of the ilium using apedicle finder; and screwing the pedicle screw into the corridor.

The pedicle screw should no not be seated completely to the bone so thatthe rigid, bowed subcutaneous fixation rod may be passed superficial tothe sartorius muscles. The rigid, bowed subcutaneous fixation rod ispreferably a titanium rod which may be bowed anteriorly.

The method further comprises subcutaneouslytunneling the anteriorlybowed rod from one of the fixation means on one ilium to another of thefixation means on the other ilium before attaching the rod. Preferablythe anteriorly bowed rod is pre-contoured with a bow and cut to theappropriate length before the step of tunneling. The anteriorly bowedrod is preferably positioned with the bow anterior to avoid anypotential compressive complications to genitourinary or neurovascularstructures prior to said step of attaching said rod. The pelvis shouldbe rotationally and vertically aligned prior to attaching the rod, andpreferably prior to tunneling the rod. Compression and tensioning of thepelvis should be performed after attaching said rod. The method furthercomprises leaving the fixation means and fixation rod attached to thepelvis for 8 to 12 weeks and thereafter removing the fixation means andthe rod.

The method may also comprising the further step of stabilizing theposterior instability prior to affixing said fixation means by insertingat least one iliosacral screw through the rear of the ilium and into thesacrum.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a diagrammatic depiction of a pelvis;

FIG. 2 shows the method in which iliosacral screws are used to performposterior stabilization of the sacroiliac joint of the pelvis;

FIG. 3 depicts a variety of iliosacral screws useful for the posteriorstabilization of the sacroiliac joint of the pelvis;

FIG. 4 depicts one embodiment of a pedicle screw system useful in theanterior pelvic stabilization surgical method of the present invention;

FIG. 5 depicts another embodiment of a pedicle screw system useful inthe anterior pelvic stabilization surgical method of the presentinvention;

FIGS. 6 a and 6 b depict yet another embodiment of a pedicle screwsystem useful in the anterior pelvic stabilization surgical method ofthe present invention; and

FIG. 7 is an x-ray of a patient who has had posterior stabilization ofthe sacroiliac joint of the pelvis using an iliosacral screw as well asthe anterior stabilization surgical method of the present inventionusing two pedicle screws and an anteriorly bowed rod.

DETAILED DESCRIPTION OF THE INVENTION

The instant invention is a novel method for definitive pelvicstabilization. The method uses the already established principles ofanterior external fixation combined with internal hardware placed in aminimally invasive fashion. Stabilization of pelvic ring injuries ismost often indicated when the volume of the pelvis is increased and/oran unstable pattern of injury is present. This stabilization method mustbe applied in the operating room under sterile conditions with adequatefluoroscopic guidance. It can be utilized in an emergent settingfollowing provisional stabilization in the emergency room with a pelvicbinder, sheet or clamp.

To aid in the determination of utilizing this anterior fixation method,we prefer the Tile classification since it is based on the concept ofpelvic stability. In the Tile classification, type A fractures involve astable pelvic ring. The partially stable type B lesions, such as“open-book” and “bucket-handle” fractures, are caused by external andinternal rotation forces, respectively. In type C injuries, there iscomplete disruption of the posterior sacroiliac complex. These unstablefractures are almost always caused by high-energy severe traumaassociated with motor vehicle accidents, falls from a height, orcrushing injuries. Type A and type B fractures make up 70% to 80% of allpelvic injuries. This fixation method is typically considered for Tile Band C type injuries. In many patients with partially stable injurypatterns, the presence of significant pain with upright posture can bealleviated with the addition of anterior fixation. Supra-acetabularfixation has been shown to have biomechanical advantages compared toiliac crest fixation. If adequate reduction cannot be obtained in aclosed manner, then more traditional open reduction techniques need tobe employed.

Surgical Technique

The patient may be positioned in the supine position on a radiolucenttable. The skin may be prepped and draped from above the umbilicus tothe proximal thigh. The lower extremity may be prepped into the field aswell to facilitate reduction techniques.

The posterior instability may be addressed first. The procedure forplacement of iliosacral screws for posterior pelvic instability has beenwell described and will not be discussed here. See for example“CT-Guided Iliosacral Screw Placement: Technique and ClinicalExperience” by Robert L. Sciulli, et al., American Journal ofRoentgenology 2007; 188:W181-W192 (reproduced athttp://www.ajronline.org/cgi/content/full/188/2/W181). FIG. 2illustrates the way in which iliosacral screws 1 are inserted throughthe rear of the ilium and into the sacrum, thus stabilizing theposterior instability. FIG. 3 depicts typical iliosacral screws 1.

After stabilizing the posterior elements via the iliosacral screws, theanterior pelvis may be addressed. A longitudinal incision (preferably2-3 cm in length) may be made centered between the Anterior InferiorIliac Spine (AIIS) and the Anterior Superior Iliac Spine (ASIS). Bluntdissection may be used through the soft tissues. Potential dangers inthis area include the lateral femoral cutaneous nerve, and care shouldbe taken not to violate the hip capsule. Fluoroscopic imaging may beused to identify the starting point of the supra-acetabular fixationscrew. The beam should be directed in an obturator oblique and pelvicoutlet direction in order to isolate the appropriate column of bone forscrew placement. A recent article by Gardner and Nork describes theappropriate placement of supra-acetabular pins in excellent detail. See“Stabilization of Unstable Pelvic Fractures With SupraacetabularCompression External Fixation”, Gardner, et al., Journal of OrthopaedicTrauma 2007; 4:269-273. Once the appropriate starting point isidentified, the cortex may be opened with a drill (preferably 5.0 mm). Apedicle finder is then used to establish a corridor between the innerand outer cortices of the ilium. Pedicle screws (preferably USS 8 mm×80mm) are placed in the supra-acetabular position under fluoroscopicguidance.

FIGS. 4, 5, 6 a and 6 b show exploded views of three different types ofpedicle screw 2 which may be useful in the method of the presentinvention. Referring to FIG. 4, the separate parts of a side-openingpedicle screw can be seen. Specifically shown are the screw 3, thesleeve 4 and the nut 5. In use, the sleeve 4 and nut 5 are placed overthe screw 3 and hold a rod in the cylindrical opening formed by themating of the screw 3 and the sleeve 4. Turning to FIG. 5, a differenttype of pedicle screw 2 is seen. In this variety, there is still a screw3, a sleeve 4 and a nut 5, but there is also a set screw 6 which helpsto hold a rod in the opening between the screw 3 and the sleeve 4.Finally, FIGS. 6 a and 6 b show a polyaxial pedicle screw having aswivel joint. Once again this variety of pedicle screw has a screw 3, asleeve 4 and a nut 5, but this type also has a mechanism consisting of aswivel clamp 7 and a swivel clamp collar 8. This added hardware allowsthe head of the pedicle screw to swivel somewhat independently from thescrew 3. Thus this swivel head allows for ease of fit to curved rods 9without the requirement for excessive rod contouring.

Returning to the surgical method, it should be noted that the screws arepreferably not seated completely to the bone so that the connecting rodmay be passed superficial to the sartorius muscles. A titanium rod 9(preferably USS 6 mm) may then be pre-contoured with a bow, placed overthe screws 2 and cut to the appropriate length on the back table. Therod may preferably be anywhere from 6 mm to 1 cm in diameter and mayalso be pre-bent for ease of use. The rod may then be tunneledsubcutaneously from one screw to the other. Before connecting the rod,it may be positioned with the bow anterior to avoid any potentialcompressive complications to genitourinary or neurovascular structures.Also, any necessary reduction may be performed at this stage. Rotationaland vertical alignment should be performed prior to attaching the rod,and preferably prior to tunneling the rod to limit pressure on the softtissues. If posterior fixation is used, then most of the reductionshould be complete at this point. This hardware system allows forcompression and tensioning once the rod is in place. Reduction andhardware position may be assessed on fluoroscopic AP, inlet and outletviews. As an alternative to fluoroscopic AP, CT guidance may be used.The construct is intended as definitive treatment, with removaltypically performed after 8 to 12 weeks. The timing of application andremoval is ultimately determined on an individual case basis.

FIG. 7 shows an x-ray of a 32-year old male who was involved in a motorvehicle accident and upon whom the inventive surgical method wasperformed. As can be seen, the posterior was stabilized and fixatedusing an iliosacral screw 1. The anterior was fixated and stabilized bythe inventive method using two pedicle screws 2, one attached to thesupra-acetabular portion of each ilium. Connected between the pediclescrews 2 is a rigid, anteriorly bowed subcutaneous fixation rod 9.

The biomechanical stability of the inventive supra-acetabular pediclescrew internal fixation construct was evaluated and compared with themore prevalent external fixator. Three different pedicle screwconstructs were compared to the external fixator, a mono axial screwsystem and two different polyaxial screw systems.

A total of 4 constructs were tested. These included: 1) an externalfixation system; 2) a mono-axial pedicle screw system; 3) a polyaxialpedicle screw system (Click'X, a trademark of Synthes Inc., West ChesterPa.); and 4) another polyaxial pedicle screw system (Pangea, a trademarkof Synthes Inc., West Chester Pa.). All constructs were assembled tohave an active length of the longitudinal element equal to 280 mm. Forthe pedicle screws systems, screws were inserted into the test blocks,leaving an approximate 15 mm gap between screw head and test block. Thisresulted in a construct moment arm of 75 mm. The external fixatorconstructs were assembled with a 145 mm construct moment arm as this iswhere the fixator connection was measured to lie in a clinical setting.

Test Apparatus

1) an MTS RT/50 Electromechancial Test Frame, from MTS Corp. (EdenPraire, Minn.), Calibrated: February 2008; and

2) an MTS Bionix Electromechanical Torsion Test Frame, from MTS Corp.(Eden Praire, Minn., Calibrated: March 2008.

Test Procedure

All constructs were tested first in axial compression. Loads wereapplied in the elastic range (20 mm displacement). Once axial testingwas completed, 3 components were tested in torsion, within the elasticrange (10°), and 2 were to failure. The three components tested withinthe elastic range (axial and torsion) were then retested in axialcompression until failure.

Axial Testing: Standard clevis fixtures were rigidly attached to theload cell and lower platen of the test machine. Constructs were mountedto the clevis fixtures using 12.7 mm diameter steel hinge pins.

An axial tensile load was applied to the construct at a test speed of 5mm/min. Load-displacement curves were acquired for each construct testedand bending yield load, stiffness and ultimate bending failure load werecalculated, as applicable. Yield load will calculation are based upon0.020×the active length (5.6 mm). Note: testing was performed for amaximum of 75 mm of axial displacement. Results are shown in Table 1.

Torsion Testing: Clevis fixtures that prevented rotation of the testblock were rigidly attached to the load cell and lower plate of the testmachine. Constructs were mounted to the clevis fixtures using 12.7 mmdiameter steel hinge pins. Spacers, that prevent test block rotationsabout the hinge pins, were manually set.

An angular displacement was applied to the construct at a test speed of60°/min. Axial load was maintained at 0 Newton. Torque-angulardisplacement curves were acquired for each construct tested andtorsional yield load, stiffness and ultimate torque will be calculated,as applicable. Yield torque was based upon a 5° offset. Note: testingwas performed for a maximum of 60° or angular rotation. Results areshown in Table 2.

TABLE 1 Summary Results - Axial Bending Stiffness Peak Yield p-valueLoad Load (vs. Ex Type (N){circumflex over ( )} (N){circumflex over ( )}(N/mm)* Fix) External 160 ± 4 102 ± 3 2.88 ± 0.05 — Fixator USS  370 ±15 *** 4.01 ± 0.11 >0.0001 Monoaxial Click'X 158 ± 1 *** 3.64 ±0.11 >0.0001 Polyaxial Pangea 137 ± 1 *** 3.63 ± 0.15 >0.0001 Polyaxial

TABLE 2 Summary Results - Torsional Peak Yield Torque Torque Torsionalp-value (N- (N- Stiffness (vs. Ex Type mm){circumflex over ( )}mm){circumflex over ( )} (N-mm/°)* Fix) External 14.70 4.92 0.50 ± 0.07— Fixator USS 5.94 4.47 0.38 ± 0.01 0.0163 Monoaxial Click'X 6.93 4.400.38 ± 0.04 0.0124 Polyaxial Pangea 6.99 5.26 0.38 ± 0.01 00055Polyaxial

The results show that the construct of pedicle screws is superior to theexternal fixator in axial loading. However, the torsional stiffness isgreater with the external fixator.

It is to be expected that considerable variations may be made in theembodiments disclosed herein without departing from the spirit and scopeof this invention. Particularly, while the invention has been describedwith respect to pedicle screws 2 that have been attached to the anteriorof each ilium and the bowed fixation rod 9 has been bowed anteriorlyaway from the pelvis, the invention can alternatively call for theattachment of the pedicle screws 2 to the posterior of the ilia and thebowed fixation rod 9 can be bowed posteriorly away from the pelvis.Accordingly, the significant improvements offered by this invention areto be limited only by the scope of the following claims.

1. A surgical method for minimally invasive treatment of unstable pelvicring injuries comprising the steps of: providing at least two fixationmeans and a bowed subcutaneous fixation rod, said bowed subcutaneousfixation rod having a first end and a second end; affixing a first ofsaid at least two fixation means to a first ilium of the pelvis and asecond of said at least two fixation means to the second ilium of thepelvis; subcutaneously tunneling said subcutaneous fixation rod from oneof said at least two fixation means on one ilium to another of said atleast two fixation means on the other ilium; attaching said first end ofsaid bowed subcutaneous fixation rod to said first of said at least twofixation means; attaching said second end of said bowed subcutaneousfixation rod to said second of said at least two fixation means.
 2. Thesurgical method of claim 1, wherein said fixation means are attached tothe supra-acetabular area between the Anterior Inferior Iliac Spine(AIIS) and the Anterior Superior Iliac Spine (ASIS) of each of the iliumof the pelvis; and said bowed subcutaneous fixation rod is tunneled in asubcutaneous arc from said first fixation means to said second fixationmeans and said bowed subcutaneous fixation rod does not arc inferior toa line between the Anterior Inferior Iliac Spine (AIIS) of each iliumand does not arc superior to a line between the Anterior Superior IliacSpine (ASIS) of each ilium.